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NMR Structure and Backbone Dynamics of the Extended Second Transmembrane Domain of the Human Neuronal Glycine Receptor α1 Subunit

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journal contribution
posted on 14.03.2003 by Victor E. Yushmanov, Pravat K. Mandal, Zhanwu Liu, Pei Tang, Yan Xu
The structure and backbone dynamics of an extended second transmembrane segment (TM2e) of the human neuronal glycine receptor α1 subunit in sodium dodecyl sulfate micelles were studied by 1H and 15N solution-state NMR. The 28-amino acid segment contained the consensus TM2 domain plus part of the linker between the second and third transmembrane domains. The presence of a well-structured helical region of at least 13 amino acids long and an unstructured region near the linker was evident from the proton chemical shifts and the pattern of midrange nuclear Overhauser effects (NOE). 15N relaxation rate constants, R1 and R2, and 15N-{1H} NOE indicated restricted internal motions in the helical region with NOE values between 0.6 and 0.8. The squared order parameter (S2), the effective correlation time for fast internal motions (τe), and the global rotational correlation time (τm) were calculated for all TM2e backbone N−H bonds using the model-free approach. The S2 values ranged about 0.75−0.86, and the τe values were below 100 ps for most of the residues in the helical region. The τm value, calculated from the dynamics of the helical region, was 5.1 ns. The S2 values decreased to 0.1, and the τe values sharply increased up to 1.2 ns at the linker near the C-terminus, indicating that the motion of this region is unrestricted. The results suggest a relatively high degree of motional freedom of TM2e in micelles and different propensities of the N- and C-terminal moieties of the transmembrane domain to assume stable helical structures.

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